The present invention relates to the vacuum tube arts. It finds particular application in connection with increasing bearing assembly life and reducing undesirable bearing assembly noise in the bearing assembly of a rotating anode x-ray tube and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable for increasing bearing assembly life and reducing unwanted bearing assembly noise in other vacuum systems.
A high power x-ray tube typically includes a rotating anode disposed within a glass envelope. A cathode supplies an electron beam to a target surface of the anode. When the electron beam strikes the rotating anode, a portion of the beam is converted to x-rays which pass out of the glass envelope.
An induction motor is typically provided for rotating the anode. The anode is configured to rotate so that the heat energy will be spread over a relatively large area, thereby inhibiting the target area from overheating. The induction motor includes driving coils positioned outside the glass envelope and a rotor within the envelope which is connected to the anode. The rotor includes an outer, cylindrical armature or sleeve and an inner bearing member, which is centrally aligned within the armature. The armature and bearing member are centrally connected to the anode by a neck. A cylindrical bearing shaft is axially aligned with the armature and bearing member and is positioned therebetween. The bearing shaft is connected, at a rearward end, to a housing disposed outside the envelope.
When the motor of a typical x-ray tube is energized, the driving coils induce magnetic fields in the armature which cause the armature and bearing member to rotate relative to the stationary bearing shaft. Bearings, such as ball or roller bearings, are positioned between the bearing member and bearing shaft for allowing the bearing member, armature, and anode to rotate smoothly, relative to the bearing shaft. The bearings are positioned between bearing grooves provided in the bearing member and bearing races provided on the stationary bearing shaft. The bearing grooves and bearing races help maintain the proper positioning of the ball bearings.
Although the bearing assemblies are manufactured with precision tolerances, there are still minor tolerance stack-ups on the order of one or two thousandths of an inch. These tolerance stack-ups create a clearance between the ball bearings and the bearing races. Thus, under the forces exerted by a relatively heavy anode (on the order of 4.5 kg), which is rotated at several thousand RPM""s (on the order of 10,000 RPM""s), the ball bearings experience unwanted movement and play. Such unwanted movement and play is also experienced when the x-ray tube is rotated such as in a CT scanner. When the ball bearings experience this unwanted movement, they tend to rub up against surfaces they are not intended to rub up against. Additionally, the clearance between the ball bearings and the bearing races permits the ball bearings to rattle back and forth. The undesirable rubbing and rattling creates bearing noise in the bearing assembly. Furthermore, rubbing and rattling reduces the life of the ball bearings.
In an attempt to overcome some of the foregoing problems, a spring member has been provided at one end of the bearing assembly. However, in such a design, the spring member pushed one set of ball bearings toward their respective bearing race and pushed the other set of ball bearings away from their respective bearing race. The ball bearings being pushed away from their bearing race still experienced unwanted rubbing. Thus, those ball bearings generated noise and had a reduced life.
The present invention provides a new and improved bearing assembly and method of operation for an x-ray tube which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, an x-ray tube for providing a beam of x-rays comprises an envelope defining an evacuated chamber. A cathode is disposed within the chamber for providing a source of electrons. An anode, disposed within the chamber, is struck by the electrons, thereby generating x-rays. A rotor is operatively connected to the anode for rotating the anode relative to the cathode. The rotor has a bearing assembly which includes a first bearing race positioned between an inner bearing member and a bearing shaft. The first bearing race has a seat for receiving a first plurality of bearings. A first biasing means applies a continuous force to the first bearing race so that the first bearing race urges the first plurality of bearings into an optimal operating position.
In accordance with another aspect of the present invention, a bearing assembly for a rotor of an x-ray tube includes a bearing shaft centrally aligned with a longitudinal axis of the rotor. An inner bearing member is concentrically spaced from the bearing shaft. A first bearing race is positioned between the inner bearing member and the bearing shaft. A first plurality of bearings are dimensioned to be received between the inner bearing member and the first bearing race. A first biasing means applies a continuous force to the first bearing race so that the first bearing race urges the first plurality of bearings into an optimal operating position.
In accordance with another aspect of the present invention, a method of reducing noise and increasing bearing life in an x-ray tube is provided. The x-ray tube has an anode rotatably connected to a rotor. The rotor has a first bearing race positioned between an inner bearing member and a bearing shaft. The rotor further includes a first plurality of bearings positioned between a seat of the first bearing race and a bearing groove defined by the inner bearing member. The method includes positioning a biasing means behind the first bearing race so that the first bearing race urges the bearings into an optimal operating position.
One advantage of the present invention is that it reduces operating noise.
Another advantage of the present invention is that it increases bearing life.
Another advantage of the present invention resides in the optimal, individual positioning of the ball bearings with respect to the bearing races and bearing grooves.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon a reading and understanding of the following detailed description of the preferred embodiment.